1. Field of the Invention
The technical field relates to a display device including an electroluminescent element (hereinafter referred to as an EL display device).
2. Description of the Related Art
In recent years, EL display devices including light-emitting elements typified by organic EL elements have been developed. EL display devices are expected to be used in a wide range of applications, using their advantages of being self light-emitting devices, such as high image quality, wide viewing angle, thinness, and lightness. In an EL display device, a light-emitting element and a transistor are provided in each pixel, and light emission of the light-emitting element is controlled with the transistor.
As a transistor for controlling light emission of a light-emitting element, a transistor including a semiconductor layer containing a metal oxide having semiconductor characteristics (hereinafter referred to as an oxide semiconductor) has attracted attention (e.g., see Patent Document 1). The luminance of the light-emitting element is proportional to the amount of current. As an example of a method for driving an EL display device, there is a driving method by which desired luminance is obtained by controlling voltage applied to a transistor and supplying current to a light-emitting element. In order to accurately express gray levels with this driving method, constant current needs to flow through the light-emitting element by controlling current by the transistor.